1. Field of the Invention
The invention relates to a rolling mill with working rolls and with multipart support rolls, said rolling mill consisting of a basic body with a plurality of rolling bearings which are arranged next to one another on the basic body in its longitudinal direction and with their outer rings rotatably support a sleeve which surrounds the rolling bearings and bears with its inner surface, all-round, on the outer surfaces of the outer rings of the rolling bearings and the outer surface of which forms the roll barrel of the support roll. Three rolling bearings, of which the middle rolling bearing is designed as a tapered roller bearing, are provided over the length of the basic body.
2. Discussion of the Prior Art
A rolling mill of this type is known from U.S. Pat. No. 1,910,158.
In present-day hot strip mills, profile and planeness control plays an important part. In this case, the negative and positive flexion of the working rolls is the "classic" actuator which, even under rolling load, allows variation. However, since the work has to be carried out, taking into account a wide variety of parameters, such as width, thickness, cross-sectional profile, material, rolling temperature, rolling speed, roll temperature and steel qualities, it is important, in the case of small batch sizes which are common nowadays and with rolling mills of universal use, to have a wide actuating range available.
In recent years, further actuators have been employed to an increased extent in new mills, the best known being the barrel contour, known as the CVC ground roll section, and the roll crossing, the crossing of the working and/or support rolls. Neither solution is optimal, because, in both methods, the rolls cannot be adjusted under load. Furthermore, the contouring of the rolls with complicated CVC ground sections has to be carried out with extreme accuracy, in order to achieve the desired geometry. Often, under particular conditions, the rolling stock undergoes different deformation at the edge and in the middle. In a continuous mill, a roll with a defined barrel contour is necessary, which is different on each stand.
In roll crossing, that is to say when the rolls of a pair of rolls are inclined relative to one another, special measures are necessary in order to achieve uniform angular speeds for a given pivoting angle. Thus, normal cardan shafts cannot be used, but, instead, toothed spindles are necessary for driving the rolls. Furthermore, pivoting generates very high axial forces which may amount to 10% of the radial rolling force. Moreover, roll crossing leads to problems in the guidance of the rolling stock, because the rolling stock rotates in the roll stand.
In the search for a further actuator which avoids the disadvantages described and is simple, support rolls with eccentrics have been developed, which are used with a sleeve of adjustable profile as an additional actuator for profile control. Thus, European patent specification 0,584,642 describes a rolling mill of the generic type, in which the round body, designated there as a roll shaft, is divided into five or more sections which are arranged eccentrically to the central axis passing through the roll shaft. The sections of the roll shaft, because of their offset, have eccentrically arranged on them support bearings in the form of tapered roller bearings, against which the cylindrical sleeve, which surrounds the rolling bearings loosely with play, can be pressed. The cylindrical portions of the sections of the roll shaft which are proposed there have different diameters which, however, are uniformly graduated symmetrically to the middle of the support roll.
During the rolling operation, the sleeve rolls, with respect to the mounting of the support roll, between the working roll and the rolling bearing outer rings facing the working roll. On the side facing away from the working roll, the sleeve runs freely without contact with the bearings. By the rotation of the roll shaft, the flexion line of the working roll can be influenced, because the effective eccentricity between the support roll and the working roll is varied. Action can thereby be taken on the profile of the roll nip in the roll stand.
A disadvantage of the known solution is that the flexing movement of the outer sleeve of the support roll between the bearings of the support roll and the working roll does not have any stability under high rolling loads. On the other hand, due to the necessary play between the sleeve and the rolling bearings of the support roll, use as the lower support roll in a hot roll stand is not possible or is possible only with great difficulty, since effective protection of the mounting against water and dirt can hardly be achieved on a permanent basis. Moreover, due to the fact that the rolling bearing outer rings come to bear only partially, the flexing movements between the sleeve and the bearing lead to marked wear phenomena which adversely influence the adjustability of the rolling mill and therefore the quality of the rolled product. Also, for the reasons mentioned, there has hitherto been no known application of a generic support roll.
Another problem of known eccentric support rolls is the mounting between the basic body and the sleeve, since the bearings have to transmit the entire rolling force. The self-aligning roller bearings provided are subjected to extremely high load and it is difficult to achieve the required service life of approximately 6,000 hours. The service life of the bearings is additionally reduced due to the eccentric adjustment between the sleeve and the basic body.
In addition, during eccentric adjustment without any rolling load, the sleeve of the support roll is deformed to an extent such that it acquires a basic convex or neutral shape. In the convex position, the self-aligning roller bearings are tilted, so that their service life is reduced even further.
Finally, in the known eccentric support roll designs, the sleeve is extremely difficult to mount, because it has to be pushed over the projecting parts of the eccentric mounting.